WHOI graduate student Michael Atkins undertook the first-ever survey to explore what kinds of single-celled protists live near deep-sea hydrothermal vents. Among his doscoveries was Ancyromonas, which may turn out to be a common ancestor from which animals and fungi first branched out from unicellular life.
(Photo by Tom Kleindinst, Woods Hole Oceanographic Institution)

In the first survey of singled-celled protozoa near seafloor hydrothermal vents, WHOI scientist Michael Atkins had expected to find new species adapted specifically to unusual vent conditions. He was surprised to find the same species of protozoa that live in surface waters, throughout the ocean depths, along coasts, in freshwater lakes, and on land.

Atkins found that under high-pressure, deep-sea conditions, protozoa can "encyst" themselves within protective cell membranes and become dormant. When conditions improve, they become active again. He speculates that hot buoyant vent plumes might deliver encysted protozoa back toward the surface where they would revive to reseed surface populations.
(Illustration by Jack Cook, Woods Hole Oceanographic Institution)

One Singular, Single-Celled Sensation

Meet one of your long-lost relatives—a distant patriarch from whom we all descend. And not just we humans. Michael Atkins suspects that lions, lobsters, mosquitoes, all fish, fowl, and fungi—every living thing besides plants that are composed of more than one cell—may all descend from the single-celled organism that he recently discovered living around hydrothermal vents on the seafloor.

Our common ancestor (the tiny guy magnified above) is called Ancyromonas, and Atkins has strong evidence that it is positioned on the evolutionary tree precisely at the momentous juncture where animals and fungi first branched out from unicellular life.

“If this organism turns out to be as important as we think it is, it holds the key to showing us what happened at a crucial evolutionary transition from unicellular to multicellular life,” he said.

Atkins found Ancyromonas in the course of research for his Ph.D., awarded in June from the MIT/WHOI Joint Program. In a way, Atkins was bound to discover something new and interesting because he undertook the first-ever survey of single-celled protists living near deep-sea hydrothermal vents.

Ever since the vents were first discovered in 1977, WHOI has led efforts to learn about the lush microbial life that thrives on sulfur-rich fluids emitted from magma-heated rocks beneath the seafloor. But those studies have focused on two of the three basic domains of life, bacteria and archaea. No one had ever explored single-celled members of the third domain: eukaryotes, which are distinguished by their nucleus-containing cells. Such deep-sea samples are notoriously difficult to collect and to culture in the laboratory.

“I had no idea what I would find,” Atkins said.

The organisms Atkins looked for are protists, single-celled eukaryotes equipped with flagella, or whip-like tails that they use to swim and to feed.

“These protists have huge ecological significance,” Atkins said. “They are integral to the marine food web. Bacteria and archaea are the most important organisms on the planet because they perform the essential biochemical reactions that convert sulfur to organic compounds, for example, or carbon dioxide to oxygen. But the organisms I work on exert important controls on the populations of bacteria and archaea by eating them.

“Protozoa consume bacteria and, in turn, are consumed by larger organisms, so they transfer energy and nutrients up the food chain,” he said. “They are also sloppy eaters, and they leave or excrete into the water dissolved, partially digested bits of bacteria—organic or inorganic materials that are used by other microbes.”

Atkins looked for protozoa in vent fluid samples collected by WHOI’s submersible Alvin. He expected to find new species that were adapted only to the unusual hot, high-pressure, high-sulfur conditions at the vents and would be found nowhere else on Earth. But to his great surprise, he mostly found the same species of protozoa that live in surface waters, throughout the ocean depths, along the coasts, and even in freshwater lakes.

“That realization led to a new hypothesis: that these organisms are ubiquitous because they have the ability to adapt to any conditions they encounter,” Atkins said.

He tested the theory in a series of laboratory experiments that exposed many types of deep-sea and shallow-water protozoa to the high-pressure and metal-rich conditions found at vents.

He was once again surprised to find no significant differences between deep-sea protozoa and those that live in shallow waters. All tolerated metal-rich fluids that would kill other life. He discovered that under high pressure, the protists “encyst”—that is, they draw in their flagella, enclose themselves within protective cell membranes, and become dormant. When Atkins reduced the pressure, the protists revived to become swimming, active participants in the food chain again.

“The findings offer an interesting theory to ponder,” he said. “Perhaps vent plumes can transfer encysted stocks of protozoa to higher levels in the water column, where the pressure is reduced and the cysts break down and the protists revive. This reversible encystment could be a mechanism to deliver protozoa back up to reseed populations that might have been decimated by adverse conditions at the surface. It would be hard and complex to prove, but if it’s true, it would have a large and important ecological significance.”

In the course of his research, Atkins used emerging molecular techniques to look for genetic differences among protozoa that are often impossible to distinguish by examining their physiology. That’s when he found Ancyromonas. Excited by the discovery, the National Science Foundation awarded Atkins a two-year postdoctoral fellowship to explore more fully its ancestral position in the tree of life. He will work with scientists at WHOI and the Marine Biological Laboratory in Woods Hole.

“It’s intriguing that this little guy could be the early ancestor of multicellular life in animals and fungi,” he said. “If we can pin that down, Ancyromonas will be very widely studied and will give us insights into where we came from and how we evolved to where we are now.”

Scientists Have Evolutionary Lines, Too.

Hydrothermal vents were discovered only in 1977, and ever since, WHOI scientists Holger Jannasch, Carl Wirsen, and others have pioneered explorations of the previously unknown microbial life that thrives in the deep sea.

“As an undergraduate, I had read about them,” said Michael Atkins. “They were my heroes.”

Atkins spent a summer as an undergraduate fellow at WHOI, and was hooked. He signed on as a graduate student and joined the lab that Jannasch led until his death in 1998.

“WHOI had the reputation for doing superb work on microbes in extreme environments and had all the tools,” he said. “It’s nice, for example, to have Alvin in your stable.

“I used to talk for hours with Holger, and Carl is a master of designing experimental methods,” said Atkins, who earned his Ph.D. in biological oceanography in June for research that included the first-ever survey of single-celled protists around vents. “The ability to be at this institution and to interact with these people, and with my advisors, Craig Taylor and Andreas Teske, has been invaluable. Craig was Holger’s first postdoctoral student and Andreas his last.”

This laboratory, like the microbes it studies, has evolutionary lines—Atkins represents the third generation.

Photo caption: Three generations of WHOI’s marine microbiology laboratory, spearheaded by the late Holger Jannasch, convene on the stern of R/V Oceanus near Cape Cod in 1996. Jannasch’s last postdoctoral student, Andreas Teske (kneeling at right), was advisor to graduate student Michael Atkins (standing far left). In between them in the front row from left to right are: Italian student Constantino Vetriani, Jannasch, WHOI Senior Research Associate Stephen Molyneaux, and German student Christian Knoblauch. In the second row, from left to right, are: WHOI Oceanographer Emeritus George Hampson, WHOI Senior Research Specialist Carl Wirsen, and Steve Aubrey of Aubrey Consulting, Inc.

Originally published: October 1, 2000

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